1. Field of the Invention
The present invention relates to a formant tracking apparatus and method, and more particularly, to an apparatus and a method of tracking a formant for non-speech vocal sound signals as well as speech signals.
2. Description of the Related Art
A formant is a frequency at which a vocal tract resonance occurs.
The disclosed conventional formant tracking methods can be divided into three types of methods.
In a first method, the formant is located on a frequency representing a peak in a spectrum such as a linear prediction spectrum, a fast Fourier transform (FFT) spectrum, or a pitch synchronous FFT spectrum. The first method is simple and fast enough to be processed in real-time. In a second method, formants are determined by matching with reference formants. The matching usually used in speech recognition is to search the reference formants best matched with the formants to be determined. In a third method, accurate frequencies and bandwidths of formants are obtained by solving a linear prediction polynomial using linear prediction coefficients.
However, a problem of the aforementioned methods is that spectral peaks for defining formants are not always clearly exist in duration because the duration for an analysis is too short to be analyzed. Another problem is that a high pitched voice increases confusion between the pitch frequency and the formant frequency. In other words, since a high frequency produces a wider interval among harmonics in comparison with a spectral bandwidth of the formant resonance, the pitch or harmonics of the pitch may be erroneously regarded as a formant. In addition, analyzed sounds may induce complicated and additive resonances or anti-resonances.